My phlegm type cough is kicking up again and i was wondering if it was safe to take my promethazine dm while on suboxone?

Talk to provider: antihistamines have significant interactions with opioids, including buprenorphine, and may cause excessive sedation. There is nothing magic about Promethazine as a cough suppressant, and you could probably get the same or similar effect just using plain Robitussin DM, and leaving antihistamines out of it, particularly phenergan, (promethazine) which really is a drug of abuse when combined with methadone.